To make the most of limited water resources, a system for purifying and re-utilizing wastewater discharged from buildings, residences, and the like has been known. For instance, Patent Document 1 discloses a wastewater re-utilization system configured to use drainage of clean water used in a household or the like and rainwater for flushing toilets, for instance, whereby it is possible to save water. Further, Patent Document 2 discloses an interior greening system for utilizing gray water, which produces gray water by processing wastewater from a building and re-utilizes the produced gray water to water plants which are grown inside a building.